The aim of our research is to test and extend a theory that accounts for cognitive changes produced by psychotropic chemicals in terms of human information processing. Information processing models in cognitive psychology attempt to isolate elementary mental operations, the concantenation of which leads to complex behavior. Our theory asserts that neurotransmitter systems differentially influence stages of information processing. The specific aim of this proposal is to determine what aspects of the aminergic neurotransmitters system affect information processing, and whether the effects are localized to specific types of processing (e.g. stimulus encoding or response selection). Behavioral and electrophysiological data will be systematically collected in accordance with a set of principles that are based on advances made in cognitive psychology, psychophysiology and neuropharmacology over the last decade. Our basic approach includes: 1) changing information processing performance by varying selected task variables, 2) collecting converging psychophysiological measures to validate separable stages of processing, and 3) controlling the activity of the aminergic neurotransmitter system through the use of aminergic agonist and antagonist agents. In short, both behavioral and electrophysiological measures are used to identify task variables that affect different processing stages. The interaction of task variables with aminergic agonists and antagonists will show the specific action of drugs on information processing and lead to predictions concerning the cognitive effects of this family of neuropharmacological agents.